Multiple, servo-controlled DC motors which are reversible to provide a driving force in either of two rotational directions, are employed in various applications, such as magnetic tape drives, for example. The motors are controlled by amplifier circuits which are pulse width modulated to provide precise motor control. In the past, the motor control circuit was implemented using a so-called "H"-bridge configuration in which the winding of the motor is connected between the legs of the "H" and each segment of the legs includes a power transistor for controlling the flow of current through the motor. Additionally, the H-bridge included four diodes which provide a path for reversed or "freewheeled" current flow from the motor to the power supply.
In order to sense the current flowing through the motor in the H-bridge, or full-bridge circuit, two sensing resistors per motor were required (which were, by necessity, physically large in order to accommodate the required power dissipation in the circuit) or a more expensive current-sensing device (e.g., a transformer) was required. Thus, the prior H-bridge configuration used a substantial number of circuit components and was relatively complicated in overall circuit design. Additionally, in some cases, the host power supply cannot accommodate the energy transferred back to the power supply during "freewheeling" diode conduction. In this event, this energy must be stored or dissipated internally in the amplifier.